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projection

@rotorsoft/act-root

@rotorsoft/act-root / act/src / projection

Function: projection()

projection<TEvents>(target?, events?): ProjectionBuilder<TEvents>

Defined in: libs/act/src/projection-builder.ts:136

Creates a new projection builder for composing read-model update handlers.

Projections enable separation of read-model concerns from command handling. Each .on({ Event }).do(handler) call registers a handler that updates a projection (database table, cache, etc.) in response to events.

Pass a target stream name to projection("target") so every handler inherits that resolver automatically. Omit it and use per-handler .to() / .void() when handlers route to different streams.

Type Parameters​

TEvents​

TEvents extends Schemas = { }

Parameters​

target?​

string

Optional default target stream for all handlers

events?​

EventRegister<TEvents> = ...

Returns​

ProjectionBuilder<TEvents>

Examples​

const TicketProjection = projection("tickets")
  .on({ TicketOpened })
    .do(async ({ stream, data }) => {
      await db.insert(tickets).values({ id: stream, ...data });
    })
  .on({ TicketClosed })
    .do(async ({ stream, data }) => {
      await db.update(tickets).set(data).where(eq(tickets.id, stream));
    })
  .build();
const MultiProjection = projection()
  .on({ OrderPlaced })
    .do(async (event) => { ... })
    .to("orders")
  .on({ PaymentReceived })
    .do(async (event) => { ... })
    .to("payments")
  .build();

See​